Environmental sealing

ABSTRACT

A sealing material preferably having a cone penetration of at least 150 (10 -1  mm) and an ultimate elongation of at least 100% is subjected to mechanical deformation by milling or chopping in the presence of a solvent or suspending medium.

This application is a continuation of Ser. No. 08/195,727 filed Feb. 14,1994, now U.S. Pat. No. 5,418,001 which is a continuation of Ser. No.07/666,552 filed Mar. 7, 1991, now U.S. Pat. No. 5,286,416, issued Feb.15, 1994 which is a continuation of U.S. Ser. No. 07/275,444 filed Nov.23, 1988, now abandoned, which is a continuation-in-part of applicationSer. No. 07/126,655 filed Dec. 1, 1987 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to environmental sealing of substrates inthe electrical, electronics, telecommunications, power and relatedindustries, particularly to sealing of electrical terminals or othercontacts and wire splices.

An environmental seal may be provided in many ways. For example, thesubstrate to be sealed may be sealed by surrounding it with some sealedbox or other enclosure, it may be tape wrapped, it may be painted or itmay be coated or surrounded with bulk sealing composition. The presentinvention is preferably concerned with this last category. Such sealingmay be provided to protect the substrate from various contaminants, andin the case of electrical contacts particularly from water.

A problem arises in providing environmental protection due to aninherent conflict between the desire for ease of installation of thesealing means, and tightness of the final seal. This problem is oftenovercome by having the sealing means undergo some change in physicalcondition, for example a paint may be applied as a liquid thatsubsequently solidifies. An alternative is the provision of athermoplastic material, such as a hot-melt adhesive, that may besoftened or melted and then applied to the substrate and allowed tosolidify. Another example is a curable composition that in its pre-curedstate has a low viscosity allowing it to be poured in place around thesubstrate, after which it is caused to cure.

For many applications, dimensionally heat-recoverable articles are usedto provide rugged, long-lasting environmental seals. Such an article maybe supplied in an expanded, enlarged, form in which it is positionedloosely around the substrate and then heated to cause it to shrink intotight engagement with the substrate.

Recently it has been proposed to provide an environmental seal by meansof a sealing material that is supplied pre-cured in some form ofcontainer which is then fixed relative to the substrate so that thesealing material is held under pressure against a surface of thesubstrate to be sealed. This technique may be contrasted with one wherea sealing material in an uncured form is poured into a container tosurround the substrate and is then cured in situ. Pre-curing has manyadvantages, particularly ease and speed of installation in the field.

An apparatus for providing environmental sealing in this way isdisclosed and claimed in U.S. Pat. No. 4,600,261 (Debbaut), thedisclosure of which is incorporated herein by reference. That patentdiscloses a protection apparatus comprising:

(a) an insulating gel characterized by

(1) a cone penetration value from approximately 150-350 (10⁻¹ mm);

(2) an ultimate elongation of at least approximately 200%;

(3) a maximum tensile strength of approximately 20 psi;

(4) a cohesive strength greater than its adhesive strength;

(b) first means to contain said gel;

(c) second means to retain said gel within said first means; and

(d) force means which acts on said first means so that said gel ismaintained in compressive contact with said electrical contact andsubstantially encapsulates a conductive portion of said electricalcontact, whereby upon release of said force means and a disengagement ofsaid first means from said electrical contact, said gel remainssubstantially within said first means.

U.S. Pat. No. 4,634,207, the disclosure of which is incorporated hereinby reference, discloses an apparatus for protecting a substrate,comprising

(a) a gel, the gel being cured prior to coming into contact with anypart of the substrate to be protected, the gel having a cone penetrationvalue of 100-350 (10⁻¹ mm) and an ultimate elongation of at least 200%;and

(b) means for deforming the gel into close and conforming contact withthe substrate.

Also disclosed is a process for protecting a substrate, comprising thesteps of:

pressing together a substrate to be protected and an apparatuscomprising a support member, a gel located on the support member, thegel being cured prior to coming into contact with any part of thesubstrate, the gel having a cone penetration value of 100 to 350 (10⁻¹mm) and an ultimate elongation of at least 200%, and means for deformingthe gel into close and conforming contact with the substrate, theapparatus and the substrate being pressed together so that the gelcontacts the substrate and is deformed into close and conforming contacttherewith.

The use of sealing materials for environmental protection is alsodisclosed in the following patents, the disclosures of each of which areincorporated herein by reference: U.S. Pat. Nos. 4,643,924 (Uken etal.), 4,690,831 (Uken et al.), 4,581,265 (Follette), 4,610,910(Follette), 4,610,738 (Jervis), 4,600,804 (Howard), 4,701,574(Shimirak), U.S. Ser. No. 901,971 filed 29 Aug. 1986 (Dubrow) equivalentto EP-A-0194872, U.S. Ser. No. 859,171 filed 29 May 1986 (Kayset)equivalent to EP-A-0225370, U.S. Pat. Nos. 4,662,692 (Uken et al.),4,647,717 (Uken), U.S. Ser. No. 767,555 (Story) filed 20 Aug. 1985equivalent to EP-A-0213874, U.S. Ser. No. 801,018 (Gamarra) filed 22Nov. 1985 equivalent to EP-A-0224389, and U.S. Ser. No. 945,219 (Chang)filed 22 Dec. 1986 equivalent to EP-A-0174165.

Cone penetration values in the above-mentioned specifications are unlessthe context otherwise requires or states, and are in this specification,expressed in units of 10⁻¹ mm and are measured by ASTM D217-68 at 70° F.(21° C.) on an undisturbed sample using a standard 1:1 scale cone (coneweight 102.5 g, shaft weight 47.5 g), the penetration being measuredafter 5 seconds.

Ultimate elongation values in the above-mentioned specifications areunless the context otherwise requires or states, and are in thisspecification, as measured according to the technique of ASTMD 638-80 at70° F. (21° C.) using a type 4 die to cut the sample and at a speed of50 cm/minute.

A problem can arise in difficult circumstances with the above prior artsealing material (referred to in general terms herein as a "gel") and/orabove prior art methods. That problem may arise where the substrate isof a complex shape since it may then be difficult to cause the gel fullyto cover all surfaces of the substrate by forcing against the substratea gel pre-cured or cast in a container. This is likely to be the casewhere the substrate is deep and must therefore penetrate a greatdistance into the gel, or where the substrate comprises many wiresaround which the gel must be caused to flow.

An alternative to pouring a liquid material around the substrate andthen curing is likely to be unacceptable because it is impractical, timeconsuming and may result in the release of undesirable gasses duringcuring. The use of a hot-melt sealing material is frequently impracticaldue to the amount of heat required, and consequent possible damage tothe substrate.

We have now found that this problem of installation of materials of thegeneral type referred to as gels can be overcome by subjecting thematerial to mechanical deformation prior to use in the presence of asuitable solvent or extender or suspending medium. This then allows thematerial to be directed to the position where it is required, by forexample extrusion through a nozzle. The step of extrusion itself mayprovide the desired mechanical deformation. We have found that the flowproperties of the material may be suitably altered by this deformation,but that it may be able, where necessary, afterwards to cohere or to"knit" back together again, retaining a sufficient ultimate elongationor other property required during its service life.

SUMMARY OF THE INVENTION

Thus, the invention provides a method of environmentally protecting asubstrate, which comprises:

(a) providing (preferably at ambient temperature) a sealing materialhaving an ultimate elongation according to ASTMD 638-80 of at least100%, preferably 200% to 300%, and a cone penetration according to ASTMD217-68 at 21° C. of greater than 100 (10⁻¹ mm);

(b) subjecting the material to mechanical deformation in the presence ofa solvent or suspending medium; and

(c) then causing (preferably at ambient temperature) the material toflow over the surface of the substrate.

The mechanical deformation preferably has the effect of breaking across-linked network of the material to create a suspension of gel orother particles. Deformation is preferably carried out in a mill, forexample using steel rollers set to a gap of say from 0.0005-0.001,preferably 0.0001-0.0005 inch.

As an alternative to a mill, the material may be deformed by choppingwith a blade or a wire.

The mechanical deformation may be carried out in the presence of asolvent such as methyl-ethyl ketone, but this may cause the material toswell with the risk of significant subsequent shrinkage. Thus, for manyuses a suspending medium that is not a solvent may be used, an examplebeing isopropyl alcohol. In any case, I prefer that the material beprocessed to produce a smooth, generally homogeneoussuspension/solution. The resulting material may be thixotropic. Thesolvent or suspending medium may be volatile liquid.

The material and the shear process are preferably such thatsubstantially no shear heat is generated.

The sealing material is preferably at least partially cross-linked, forexample at least 0.01 to 6 cross-links per weight average molecule, morepreferably 0.5 to 4, especially 0.5 to 2 cross-links

A container may be provided around the substrate, into which thematerial is directed, preferably by extrusion from a material-dispensinggun, for example of the general type known as a grease-gun.Alternatively, the material may be extruded or otherwise directed intothe container, and the container with the material then positionedaround the substrate. We have found surprisingly that when the containeris thus positioned with respect to the substrate, the sealing materialflows (for example by folding or rolling) around the substrate causingit to be covered in a most satisfactory way. This may be compared to thecovering that is achieved with similar gel materials that have notundergone shear. In that case the material appears to have a skin thatfirst stretches and finally breaks, but even then the material may notproperly squeeze back over the substrate without excessive trapping ofair.

The effect of shear in allowing such materials to be directed byextrusion or otherwise, but to retain their elongation or elastic memoryor other properties, was quite unexpected. Also unexpected was theeffect of shear in improving the ability of such materials prepositionedin a container to be deformed around a substrate. Shear preferablycauses the material to be fragmented, which may be regarded as causingcomminution, fracture, or brecciation, or chopping, depending on thesize and size distribution of resulting particles. Small particles arepreferred.

The effect of deformation of the material may be regarded ascomminution. Its flow properties are thereby improved. In the case ofgels as referred to above, the resulting material may be regarded as anagglomeration of particles, each comprising a cross-linked networkcontaining an uncross-linked or liquid component, the particles beingloosely interconnected by adhering together, possibly by autoadhesion.Before the mechanical deformation the material may be regarded as asingle cross-linked network containing the uncross-linked or liquidcomponent. This change may be reflected in an increase in it G" value,G" being its loss modulus as determined by dynamic spectroscopy. Thematerial may then be directed as desired by extrusion etc.

The invention therefore also provides a method of producing a sealingmaterial which comprises:

(a) providing a material having an ultimate elongation according to ASTMD638-80 of at least 100%; and

(b) fragmenting the material in the presence of a solvent or suspendingagent.

Compression preferably occurs during extrusion, and this can be enhancedby correct choice of extrusion nozzle size and land length.

We have found also that advantageous sealing materials, particularly forthe installation techniques disclosed herein, have a lower stressrelaxation than that of otherwise similar prior art gel.

Stress relaxation is to be performed at 23° C. for 1 hour using adynamic spectrometer (such as Rheometrics RDS-770, trade mark) in thetransient parallel plate mode. A stress relaxation ratio may be deformedas the ratio of the stress, or modulus, G(T), at time t divided by peakstress achieved when the strain is applied at time t=0. The stressrelaxation time is therefore the time at which the stress relaxationratio is equal to, ie. 0.368; describing the exponential decay of anidealized stress relaxation curve.

We prefer that the sealing material has a stress relaxation time of lessthan 800 seconds, more preferably less than 700 seconds, particularlyless than 500 seconds.

Sealing material may be supplied in any convenient way. For some usesthe material may be extruded from a material-dispensing gun, and theinvention therefore further provides a cartridge (optionally adisposable cartridge) having therein a cured material having an ultimateelongation of at least 100% according to ASTM D638-80 and a conepenetration value of 150-350 (10⁻¹ mm).

The sealing material of the invention or used in a method or article ofthe invention preferably has one or more of the following properties

Cone penetration

The cone penetration of the material before use is preferably greaterthan 100, more preferably greater than 150, particularly greater than170, especially greater than 200 (10⁻¹ mm). It is preferably less than400, more preferably less than 350, especially less than 300 (10⁻¹ mm).

Ultimate elongation

The ultimate elongation of the material before use is preferably greaterthan 50%, more preferably greater than 100, particularly greater than200%, more particularly greater than 300%.

Storage modulus (G')

Storage modulus of the material before use is determined by dynamicspectroscopy (using for example a Rheometrics RDS-7700, trade mark)measured at 24° C. on a 25 mm diameter disc at 1 Hz frequency. G' ispreferably less than 10⁷ dynes/cm², more preferably less than 5×10⁶dynes/cm², particularly less than 10⁶ dynes/cm², especially less than5×105 dynes/cm2

Tan delta

Tan delta of the material before use is the ratio between the lossmodulus (G") and the storage modulus (G'), each in dynes/cm2, eachdetermined by dynamic spectroscopy. Tan delta is preferably less than 1,ie. the storage modulus is preferably greater than the loss modulus.More preferably tan delta is less than 0.8, particularly less than 0.7.

Stress relaxation time

For the material after deformation, this is preferably less than 900seconds, more preferably less than 700 seconds, particularly less than500 seconds, especially less than 200 seconds Preferably it is greaterthan 10 seconds, particularly greater than 50 seconds It is desirablethat the material relax as fast as possible initially (so that thematerial can easily surround a substrate) and then not relax further, sothat it can be put and remain under compression.

Tack

The sealing material before and after deformation is preferably tacky,more preferably has high tack.

The means for mechanically deforming and for dispensing the sealingmaterial preferably have one or more of the following characteristics.

The material and the means for dispensing are preferably such that thematerial can be dispensed under a pressure of less than 100 psi, morepreferably less than 50 psi, particularly less than 20 psi, particularlyless than 10 psi.

The flow rate of the material from the means for dispensing ispreferably greater than 0.01 grams per second, more preferably greaterthan 0.1 grams per second, particularly greater than 1.0 grams persecond, especially greater than 10 grams per second.

The material may be extruded through a nozzle of diameter greater than0.075 cms, preferably greater than 0.1 cm, preferably greater than 0.2cm. A smaller nozzle helps to stick the particles of comminuted materialback together.

The nozzle land preferably has a length of at least 1 cm, morepreferably at least 2 cm, particularly at least 3 cm. The land throughwhich the material passes after deformation helps to cause pressure orflow orientation or gives the material time to relax some of itsoriginal memory before pressure reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a material-dispensing gun.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a material dispensing gun containing a sealing materialthat has been subjected to milling in the presence of a solvent orsuspending agent.

The sealing material is usually electrically insulating (ie. has aresistivity of at least 10⁹ ohm.cm), but is not necessarily so for somepossible uses of the invention, e.g. when non-electrical substrates arebeing protected. Suitable sealing materials include materials made bygelling curable polyurethane precursor materials (as described forexample in the patents referenced above in the presence of substantialquantities of a mineral oil, a vegetable oil or a plasticizer, or amxiture of two or more of these. Thus we have obtained excellent resultsusing sealing materials prepared by gelling components which arecommercially available for the preparation of polyurethane gels in situ,the gelation being carried out, however, in the presence of a suitableamount, e.g. 30 to 70% by weight, of a suitable plasticizer, e.g. atrimellitate, or in the presence of a suitable animal or vegetable oil,e.g. 80 to 60%, preferably 80 to 70%, by weight of a mixture of mineraland vegetable oils in which the ratio by weight of mineral oil tovegetable oil is 0.7 to 2.4. Suitable sealing materials can also beprepared by curing reactive silicones with non-reactive extendersilicones, and the invention includes the use of any sealing materialhaving the desired cone penetration and elongation values. The sealingmaterial may contain known additives such as moisture scavengers (e.g.benzoyl chloride), antioxidants, pigments and fungicides. The sealingmaterial is preferably hydrolytically stable, moisture-insensitive, andsubstantially inert towards the substrate.

We claim:
 1. A method of environmentally protecting a substrate whichcomprises:(a) providing a sealing material having an ultimate elongationaccording to ASTM D638-80 of at least 100% and a cone penetrationaccording to ASTM D217-68 at 21° C. of greater than 100 (10⁻¹ mm); (b)subjecting the material to mechanical deformation in the presence of asolvent or suspending medium; and (c) then causing the material to flowover a surface of the substrate.
 2. A method according to claim 1, inwhich the material has a cone penetration value of at least 150 (10⁻¹mm).
 3. A method according to claim 1, in which the material aftersubjection to shear, has a stress relaxation time, being the time atwhich the stress relaxation ratio is equal to e⁻¹, of less than 900seconds.
 4. A method according to claim 1, in which the materialprovided has a tan delta value, being the ratio of loss modulus tostorage modulus as determined by dynamic spectroscopy, of less than 1.5. A method according to claim 1, in which the material is subjected toshear by milling.
 6. A method according to claim 1, in which thematerial is subjected to shear in the presence of a suspending mediumthat is not a solvent for that material.
 7. A method according to claim1, in which the material is mechanically deformed in such a way as toincrease its G" value, G" being its loss modulus as determined bydynamic spectroscopy.
 8. A method according to claim 1, in which thematerial provided is cross-linked.
 9. A method according to claim 1, inwhich the substrate comprises an electrical terminal or wire splice. 10.A method according to claim 1, which additionally comprises maintainingthe material under pressure against the surface.
 11. The methodaccording to claim 1 wherein the sealing material is a cross-linkedsilicone gel sealing material and has a cone penetration value beforeuse of at least 170 (10⁻¹ mm) to less than 400 (10⁻¹ mm) and anelongation of greater than 200%.
 12. A method of environmentally sealinga substrate which comprises:(a) providing a sealing material having anultimate elongation according to ASTM D638-80 of at least 100% and acone penetration according to ASTM D217-68 at 21° C. of greater than 100(10⁻¹ mm); (b) providing a container around the substrate; (c)subjecting the material to shear; and (d) placing the material into thecontainer such that it surrounds the substrate.
 13. A method accordingto claim 12, in which:(a) the material is subjected to shear, (b) thecontainer is provided around the substrate; and (c) then the material isplaced into the container.
 14. A method according to claim 12, inwhich:(a) the material is subjected to shear; (b) then the material isplaced into the container; and (c) then the container with the materialtherein is positioned around the substrate.
 15. The method according toclaim 12 wherein the sealing material is a cross-linked silicone gelsealing material and has a cone penetration value before use of at least170 (10⁻¹ mm) to less than 400 (10⁻¹ mm) and an elongation of greaterthan 200%.
 16. A method of producing a sealing material, whichcomprises:(a) providing a material having an ultimate elongationaccording to ASTM D638-80 of at least 100% and a cone penetrationaccording to ASTM D217-68 at 21° C. of greater than 100 (10⁻¹ mm); and(b) milling the material in the presence of a solvent or a suspendingmedium.
 17. The method according to claim 16 wherein the sealingmaterial is a cross-linked silicone gel sealing material and has a conepenetration value before use of at least 170 (10⁻¹ mm) to less than 400(10⁻¹ mm) and an elongation of greater than 200%.